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Cross-Linked Polyethylene Tubing & Water Contamination

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Michael Fox, PhD.



Cross-Linked Polyethylene Tubing and Water Contamination

During 2001, families that had just purchased newly constructed custom homes valued at about a half million dollars or more noticed that their drinking water smelled and tasted strange. The odor was reminiscent of gasoline. Chemaxx was brought in to investigate the source of the chemicals. First, it was determined that the incoming water from the city was clean. Therefore, the chemical contamination was originating from somewhere in the home itself.

In the course the investigation it was discovered that t-butanol and MTBE were showing up in the water. The levels of t-butanol spanned a broad range, but in homes where the water had been stagnant for a period of time the concentrations were as high as 10,000 ppb and greater. For comparison, the State of California has an enforceable Maximum Contaminant Level (MCL) on MTBE of 13 ppb, and a non-enforceable Action Level on t-butanol of 12 ppb. Click here for a summary of the maximum concentrations found for various chemicals in the drinking water.

It was noted that t-butanol and MTBE were fingerprints for gasoline. Therefore, a number of scenarios were investigated, including ground water contamination, accidental contamination during construction or sabotage.

It turned out that the homes had been plumbed with cross-linked polyethylene tubing, commonly and generically referred to as PEX. After considerable investigation that included several dead-end scenarios, it was determined that the source of these two chemicals was the tubing itself.

One method of cross-linking polyethylene tubing is via the catalyst t-butyl peroxide. The t-butanol and MTBE are breakdown products of the t-butyl peroxide. The t-butanol was significantly more predominant than the MTBE. A methyl group is obviously picked up from the tubing somehow in order to form the MTBE.

Since the chemicals enter the water via a diffusion process, the concentrations were a function of how long the water was in contact with the tubing. Long periods of stagnation favored high levels of the chemicals while frequent and regular use of the water lines favored lower concentrations. With time, the chemicals are eventually washed out of the tubing. Research was also conducted to determine exactly how long they persist.

Chemaxx has learned about another potential problem with PEX tubing. Evidently, rodents in search of water may chew through the tubing, thereby causing leaks, which in turn can create water damage and mold. Therefore, rodent protection must be maintained to a high degree of certainty where PEX is used.

Note: There are different ways to cross-link polyethylene and not all types of cross-linked polyethylene tubing contain t-butyl peroxide. Such tubing would not be expected to contribute MTBE or t-butanol to the drinking water. Also, the data above pertained to PEX tubing manufactured during 2001 or earlier. It is Chemaxx's understanding that some producers of PEX may have altered their manufacturing processes, and what was found in 2001 may not apply today. However, if t-butanol and/or MTBE are showing up in the drinking water of newly constructed homes with PEX tubing, there is a possibility that it is coming from the PEX tubing. In fact, preliminary experiments conducted on PEX tubing purchased on November 23, 2004 produced results reminiscent of the 2001 experience.

Recommendation: If you plan to move into a new home plumbed with PEX tubing, or have recently done so, and if you are concerned about the possibility of chemicals entering the drinking water, you might want to flush all the lines daily for 1-2 minutes for the first 3-6 months and perhaps once a week for the next 6-12 months. Another helpful approach is to install a reverse osmosis water purification system for drinking water and ice makers. Both flushing and reverse osmosis are recommended.

If you are considering whether to build your home with PEX, you might ask the PEX manufacturer for a written letter that clearly states whether chemicals will be added to the drinking water and if so, which chemicals and to what degree. Note that simply passing NSF Standards does not guarantee that chemicals will not be added to your drinking water. Click here to see letters written to NSF by Dr. Fox. NSF used to be called the National Sanitary Foundation.

Dr. Fox is a chemical expert, with extensive experience in OSHA chemical regulations and chemical safety. He also has extensive knowledge and considerable field data concerning cross-linked polyethylene tubing (PEX).